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Status:

PROPOSED STANDARD

Updates:

RFC 7252

Updated by:

RFC 8323

Authors:

C. Bormann
Z. Shelby, Ed.

Stream:

IETF

Source:

core (wit)

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DOI:  https://doi.org/10.17487/RFC7959

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Abstract

The Constrained Application Protocol (CoAP) is a RESTful transferprotocol for constrained nodes and networks. Basic CoAP messageswork well for small payloads from sensors and actuators; however,applications will need to transfer larger payloads occasionally --for instance, for firmware updates. In contrast to HTTP, where TCPdoes the grunt work of segmenting and resequencing, CoAP is based ondatagram transports such as UDP or Datagram Transport Layer Security(DTLS). These transports only offer fragmentation, which is evenmore problematic in constrained nodes and networks, limiting themaximum size of resource representations that can practically betransferred.

Instead of relying on IP fragmentation, this specification extendsbasic CoAP with a pair of "Block" options for transferring multipleblocks of information from a resource representation in multiplerequest-response pairs. In many important cases, the Block optionsenable a server to be truly stateless: the server can handle eachblock transfer separately, with no need for a connection setup orother server-side memory of previous block transfers. Essentially,the Block options provide a minimal way to transfer largerrepresentations in a block-wise fashion.

A CoAP implementation that does not support these options generallyis limited in the size of the representations that can be exchanged,so there is an expectation that the Block options will be widely usedin CoAP implementations. Therefore, this specification updatesRFC 7252.

For the definition ofStatus,seeRFC 2026.

For the definition ofStream, seeRFC 8729.